1. Technical Field
The present disclosure relates to electrosurgical apparatuses, systems and methods. More particularly, the present disclosure is directed to an electrosurgical control system that provides improved power curve transition response.
2. Background of Related Art
Energy-based tissue treatment is well known in the art. Various types of energy (e.g., electrical, ultrasonic, microwave, cryogenic, heat, laser, etc.) are applied to tissue to achieve a desired result. Electrosurgery involves application of radiofrequency (RF) electrical current to a surgical site to cut, ablate, coagulate or seal tissue.
In bipolar electrosurgery, one of the electrodes of the hand-held instrument functions as the active electrode and the other as the return electrode. The return electrode is placed in close proximity to the active electrode such that an electrical circuit is formed between the two electrodes (e.g., electrosurgical forceps). In this manner, the applied electrical current is limited to the body tissue positioned between the electrodes. When the electrodes are sufficiently separated from one another, the electrical circuit is open and thus inadvertent contact with body tissue with either of the separated electrodes does not cause current to flow.
Bipolar electrosurgical techniques and instruments can be used to coagulate blood vessels or tissue, e.g., soft tissue structures, such as lung, brain and intestine. For example, a surgeon can cauterize, coagulate, desiccate, or simply reduce bleeding, by controlling the intensity, frequency and duration of the electrosurgical energy applied between the electrodes and through the tissue. In order to achieve one of these desired surgical effects without causing unwanted charring of tissue at the surgical site or causing collateral damage to adjacent tissue, e.g., thermal spread, it is necessary to control the output from the electrosurgical generator, e.g., power, waveform, voltage, current, pulse rate, and so forth.
In monopolar electrosurgery, the active electrode is typically a part of the surgical instrument held by the surgeon that is applied to the tissue to be treated. A patient return electrode is placed remotely from the active electrode to carry the current back to the generator and safely disperse current applied by the active electrode. The return electrodes usually have a large patient contact surface area to minimize heating at that site. Heating is caused by high current densities which directly depend on the surface area. A larger surface contact area results in lower localized heat intensity. Return electrodes are typically sized based on assumptions of the maximum current utilized during a particular surgical procedure and the duty cycle (i.e., the percentage of time the generator is on with respect to total procedure time).
Electrosurgical generators are typically comprised of power supply circuits, front panel interface circuits, and RF output stage circuits. Many electrical designs for electrosurgical generators are known in the field. In certain electrosurgical generator designs, the RF output stage can be adjusted to control the output power. The methods of controlling the RF output stage may comprise changing the duty cycle, or changing the amplitude of the driving signal to the RF output stage. The RF output may be characterized by RMS or peak-to-peak voltage, power, and/or current.
One of the effects that may be associated with electrosurgical desiccation is undesired tissue damage due to thermal effects, or thermal spread. Thermal spread may occur when healthy tissue adjacent to the operative site is undesirably affected because much too heat is allowed to build up at the operative site. Such heat may conduct to adjacent tissue and cause a region of necrosis in adjacent tissue. Thermal spread becomes a particular concern when electrosurgical tools are used in close proximity to delicate anatomical structures. Therefore, an electrosurgical generator that can better control the application of energy may reduce the occurrence or severity of thermal spread, which, in turn, may provide improved surgical outcomes and reduced operative times.
Another effect that may be associated with electrosurgical desiccation is a buildup of deposits, known as eschar, on the surgical tool. Eschar is created from tissue that is desiccated and then charred by heat. The surgical tools may lose effectiveness when the electrodes thereof become coated with eschar during use. The buildup of eschar may be reduced by controlling the heat developed at the operative site.
Arcing is yet another effect that may be associated with electrosurgical desiccation. Arcing is known in the art to be effective in cutting or dissection procedures, and may be desirable in monopolar cut modes and/or monopolar coagulation modes. However, arcing is usually undesirable in bipolar coagulation modes and/or bipolar vessel sealing modes.
Practitioners have known that a measurement of electrical impedance of tissue is a good indication of the state of desiccation of tissue, and/or the presence or absence of arcing between an electrode to tissue. Several commercially available electrosurgical generators can automatically adjust output power based on a measurement of impedance. Several methods for controlling output power in response to tissue impedance have been developed. Such control methods may exhibit uneven power delivery, such as power discontinuities and waveform distortion (e.g., glitching) when output power adjustments are performed.